1. Field of the Invention
The present invention relates to a patch antenna and a wireless communications device.
2. Description of the Related Art
Conventional wristwatch-type wireless terminals have a problem of degradation in antenna characteristics due to influence from a wrist where the wireless terminal is attached, for example.
For this reason, such a wireless terminal uses a patch antenna which has directivity in the zenith direction with respect to the GND surface thereof and is less influenced by a wrist where the wireless terminal is attached.
The patch antenna includes a dielectric body, a radiation element disposed on the top surface of the dielectric body, and an earth conductor disposed on the bottom surface of the dielectric body.
The technique of such a patch antenna is disclosed in, for example, Japanese Unexamined Patent Application Publication No. 2002-198725.
In general, a patch antenna occupies a larger space than other electronic components built in a wristwatch-type wireless terminal.
For this reason, in a wristwatch-type wireless terminal, a patch antenna is often mounted not in a main body case, where many electronic components are disposed and where there is not a sufficient space for the patch antenna, but in a band attaching portion, which affords more space for the patch antenna.
FIG. 12A is a plan view of a conventional wristwatch 600, and FIG. 12B is a side view thereof, a part of the wristwatch 600 cut out.
The wristwatch 600 includes a main body case 601, to which band attaching portions 601a and 601b are attached, and bands 602a and 602b attached to the band attaching portions 601a and 601b. 
The main body case 601 and the band attaching portions 601a and 601b are formed in one united body with resin.
In the main body case 601, a GPS (global positioning system) module as a communication module is mounted, for example.
The band attaching portions 601a and 601b each have the shape of an isosceles trapezoid when viewed from above. More specifically, the widths of the band attaching portions 601a and 601b decrease in the direction from the main body case 601 toward the bands 602a and 602b, respectively.
Further, the bottom surfaces of the band attaching portions 601a and 601b are flush with the bottom surface of the main body case 601. The thicknesses (i.e., the heights of the top surfaces) of the band attaching portions 601a and 601b increase in the direction from the bands 602a and 602b, respectively, toward the main body case 601.
The band attaching portion 601a which is at the 6 o'clock position (i.e., 6 o'clock position of the analog watch) serves as an antenna case. A patch antenna 610 is encased within the band attaching portion 601a. 
The expression “a patch antenna 610 is encased within the band attaching portion 601a” means a state where the patch antenna 610 is fitted (contained) in the band attaching portion 601a without protruding therefrom.
The patch antenna 610 has the shape of a square prism, and appears to be a square when viewed from above.
Further, the patch antenna 610 has a uniform thickness (i.e., constant height of the top surface).
The lengths of sides and thickness of the patch antenna 610 are constrained and determined on the basis of the smallest dimension within the space of the band attaching portion 601a. 
Specifically, the lengths of sides of the patch antenna 610 are determined in accordance with the depth (i.e., the distance between the main body case 601 and the band 602a) of the band attaching portion 601a, the depth being smaller than its width; and the thickness of the patch antenna 610 is determined in accordance with the smallest height of the band attaching portion 601a. 
Therefore, when the depth and the smallest height of the band attaching portion 601a are small, the size of the patch antenna 610 is restricted in accordance with the depth and the height. This reduces the volume of antenna, resulting in insufficient sensitivity characteristics (antenna gain).